okay so i have been working on this thing for over two months now. I originally was only going to change the timing belt on my 2009 Subaru outback. I changed it and put everything back together but it wouldn't start. I took it back apart and changed the valves because they were bent, and changed the head gaskets, exhaust gaskets, intake gaskets, and the spark plugs. I put it back together and lined the timing marks and now it will not start it only backfires... it will crank but it doesn't fully start just backfires. 

If you are sure the crank and cam sensors are attached, I would look at the gas.

Having a similar issue with a rebuilt ej25d, and it's been sitting outside for about 3 mos.

Sprayed carb cleaner in the intake and it wants to catch, but....

 On way now to siphon the 1/4 of tank in there and put a few gallons of premium in to get it running.

 

O.

If its backfiring the timing is wrong.

 

Timing notch on the crank sprocket is on the back edge. Should line up with the notch in the housing the crank sensor sits in. Keyway should be at 6 o'clock.

 

Cam notches line up with the vertical seam in the head.

Arrows on the cam sprockets will point at 1:30 when the notch is in the right spot.

You should be hand turning the engine over w/o the plugs in so it'll turn easier and checking for piston to valve interference BEFORE ever cranking it. Like Fairtax stated, it's probably not aligned correctly. But it's also possible you bent more valves again.

 

Get the belt on correctly (google "Subaru timing belt removal/installation" for visuals on how to line it up; DOHC is a little more involved than SOHC if that's what you have) then do a compression test of each cylinder to make sure you don't have a valve stuck.